The present invention relates to spectral analysis of electromagnetic radiation and, in particular, devices for simultaneously determining the direction and wavelength of an incident monochromatic light beam.
It is known to use dispersive techniques for analyzing electromagnetic radiation. In the context of modern weapons systems, the use of lasers has become widespread. The need to warn vehicle operators and the like of the presence and origin of incident laser radiation has lead to the development of various devices intended to use dispersive techniques to identify incident laser radiation.
U.S. Pat. No. 4,682,888 to Welner discloses a spectral analyzer and direction indicator. The device uses a non-diffracted beam and two detector arrays to determine the direction of incidence of the radiation, and two reflection gratings with a further three detector arrays to provide information for spectral analysis.
U.S. Pat. No. 4,674,871 to Shifrin discloses a spectral analyzer and direction indicator. The device uses two reflection gratings arranged at 90.degree., each having a lens with a detector array at the focal plane. In order to provide full directional information, a double apparatus with four gratings with their associated optical systems and detector arrays is required. The field of view (FOV) of the device appears to be about 30.degree. wide.
U.S. Pat. No. 5,043,726 to Shifrin discloses a spectral analyzer and direction indicator. The device uses two orthogonally mounted optical channels each having a reflector partially ruled with a diffraction grating. Each channel is provided with an optical system having a detector array at its focal plane. The FOV of the device is about 10.degree.-20.degree. wide.
All of the devices disclosed in these patents share a number of shortcomings. Firstly, each of the devices includes a large number of optical elements which must be maintained in precise geometrical and angular alignment to ensure correct operation. This makes them expensive to produce, oversized, and susceptible to inaccuracies and malfunctioning due to misalignments. Secondly, the design of each of the devices imposes severe geometrical limits on its operative field of view.
There is therefore a need for a spectral analyzer and direction indicator for simultaneously determining the direction and wavelength of an incident light beam which is structurally simple, compact and inexpensive, and which has a wide operational field of view.